1. Field of the Invention
The present invention relates to a distance correcting apparatus of a surroundings monitoring system for correcting distance information containing errors caused by a positional deviation of a stereoscopic camera and to a vanishing point correcting apparatus of the system.
2. Discussion of the Background Art
In recent years, a stereoscopic surrounding monitoring apparatus using a pair of left and right cameras, that is, a stereoscopic camera, having solid image element like CCD mounted on a vehicle and the like has been watched by concerned engineers. To detect a distance to an object, first respective pixel blocks having coincidence of brightness are found in left and right images (stereo matching), then distance data are calculated according to the principle of triangulation from a parallax, namely a relative deviation amount, between both pixel blocks. Consequently, in order to calculate distance data with high reliability, it is desirable that there exists no positional deviation other than the parallax in a pair of left and right images (stereo images). In actual world, however, the stereoscopic camera has some amount of positional errors such as horizontal or vertical deviations (parallel deviations), a rotational deviation and the like, caused when the camera is installed on a vehicle and the like. Particularly, the horizontal deviation directly produces an error in an parallax and as a result the distance calculated based on the parallax differs from a real one.
With respect to this, Japanese Patent Application Laid-open No. Toku-Kai-Hei 10-307352 discloses a technology in which the positional deviation of the stereoscopic camera is corrected by applying a geometric transformation to the stereoscopic image. That is, when an initial adjustment of the positional deviation is made or when a readustment of the positional deviation generated by aged deterioration is made, a dedicated correction detecting device is connected with an image correction apparatus performing the affine transformation to calculate the difference of angle of view, a rotational deviation or a parallel deviation of the stereoscopic image obtained by imaging a specified pattern for adjustment and to establish (reestablish) parameters of the affine transfomation according to the result of the calculation. The positional deviation is equivalently corrected by applying the affine transformation to images based on thus established affine parameters.
However, according to the aforesaid prior art, a special adjustment pattern is imaged by the stereoscopic camera and the deviation is corrected based on the position of the pattern in images. Accordingly, when the correction is performed, it is necessary to interrupt the ordinary surroundings monitoring control and as a result this prior art is not suitable for a real time processing in which the monitoring control is carried out concurrently.